Titanium and titanium alloys have been used as base materials of implants which are placed in living bodies, such as dental implants, for their high biocompatibility, resistance to corrosion, and mechanical strength. However, when a dental implant made of titanium and the titanium alloy is directly fixed to a jaw bone, metabolism in restoring osseous tissue of the jaw bone gets out of balance, and the dental implant may be loosened, or osteolysis of the jaw bone may occur.
A cause of the dental implant failure is peri-implantitis which may lead to osteolysis by osteoclasts induced around the dental implant. The peri-implantitis may be derived from microbial stimulus such as bacterial infection etc., and mechanical stimulus such as excessive occlusal force etc., and may also be caused by activation of the osteoclasts by the dental implant itself.
The activation of the osteoclasts by the dental implant occurs in an early stage after the placement of the implant. The osteoclasts induced in the early stage inhibit osseointegration of the implant, which leads to implant failure.
A presumable cause of the activation of the osteoclasts is that titanium and the titanium alloy do not have sufficient affinity for bone cells. On a surface of a material which does not have sufficient affinity for the bone cells, differentiation from osteoclast precursor cells to the osteoclasts is accelerated to cause osteolysis. It has been known that titanium and the titanium alloys have relatively high affinity for the bone cells. However, their affinity is not sufficient, and the dental implant failure may occur depending on conditions of the jaw bone and an oral cavity of a subject.
To improve the affinity for the bone cells, coating the implant such as the dental implant etc. with a diamond-like carbon thin film (a DLC film) has been attempted (see, e.g., Patent Document 1). The DLC film has high biocompatibility because a main component thereof is carbon, and a surface thereof is smooth and inactive. For these reasons, the DLC film presumably has high affinity for the bone cells.